The present invention is related to a method for printing a franking mark on a document, comprising the following steps:    a. making available a unique bit string;    b. establishing an identification code;    c. securely printing said franking mark on the document, said franking mark at least comprising information relating to the bit string and the identification code.
“Franking mark” here refers, for example, to an electronic postage stamp, that is to say a mark printed on a postal article by a franking machine or a printer, which inter alia can represent a franking value for said postal article. In the context of the present invention, however, “franking mark” has a wide meaning. The concept “franking mark” can refer to all kinds of marks which can be placed on arbitrary documents for securing said documents. Besides postal articles, such documents can also be value documents, such as admission tickets, payment slips, etc., which are protected by such a mark.
A method of the kind mentioned in the beginning is disclosed in the following two documents made public by the Engineering Center for United States Postal Service (USPS): “Information Based Indicia Program (IBIP), Open System Indicium Specification” and “Information Based Indicia Program (IBIP), Open System Postal Security Device (PSD) Specification”, both dated 23 Jul. 1997 (draft documents)
With such a method, electronic postage stamps can be obtained and printed on postal articles. The device, for example a computer, with which the electronic postage stamp is printed is thereto provided with a Postal Security Device (PSD), to which a unique identification code is related. The electronic postage stamp comprises various elements, of which a few are mentioned as “security critical”: the identification code of the PSD, the value of the contents of an incremental register, the franking value of the postal article and a digital signature. The contents of the incremental register represent the total monetary value of all hitherto printed electronic postage stamps with the related PSD. The combination of identification code and the contents of the incremental register represents a unique bit string per postal article. Since the manner in which said unique bit string is composed must comply with a known rule, the value of a following unique bit string for a following electronic postage stamp can be predicted, which is disadvantageous in regard to possible fraud.
In an article by J. Quittner in FOX Market Wire of 9 Apr. 1998, “Neither bugs, nor hackers, nor Pitney Bows will keep E-stamp from delivering your postage”, available on the Internet on 5 May 1998, such a system, which meets these specifications and originates from the firm of E-Stamp, is described. The system of E-Stamp also makes use of a personal computer for printing a franking mark on a postal article directly with the aid of a regular printer connected to said personal computer. The personal computer is connected, via the Internet, with the United States Postal Service. Via the Internet, “electronic postage stamps” can thus be bought at the United States Postal Service. The franking value of the electronic postage stamp is debited directly from the savings balance of the related client and stored and protected in the PSD. The PSD is a small box which can be inserted at the rear of a regular laserprinter. As soon as a user has issued a command to print an electronic postage stamp on a postal article, an electronic postage stamp is downloaded and the printer prints a two-dimensional bar code, after which the value of the printed “postage stamp” is debited from the total franking value is debited in the postal security device.
According to the publication of J. Quittner, the electronic postage stamp in the system of E-Stamp comprises in any case an identification code of the user, an identification code of the postal security device, the franking value, the delivery type (for example by express delivery), the sender's address and the date. The electronic postage stamp can further also contain data related to the sending company, and room is provided for possible advertisements.